Testate amoebae are informative bioindicators of critically high ammonia deposition on peatlands

The global nitrogen cycle has been majorly disrupted by anthropogenic activity. While nitrogen emissions in the UK and Ireland are declining, ammonia (NH3) remains a significant exception. NH3 emissions are mostly agriculturally sourced and deposited on nearby habitats at high rates in both countries. Peatlands are globally important wetlands that are vulnerable to NH3 deposition. Essential peatland restoration risks being diminished by excessive NH3 deposition, leading to the loss of valuable ecosystem services. This study investigates testate amoebae (indicators of contemporary and historic peatland conditions) as bioindicators of seasonal NH3 deposition on six peatlands across Northern Ireland, UK. Sphagnum, an NH3-sensitive bryophyte, was sampled adjacent to NH3 monitoring sites once per season for a year. When NH3 deposition was critically high, multivariate analysis demonstrates a link between NH3 and testate amoebae assemblage change. Similarly, at high NH3 deposition sites, testate amoebae taxa diversity is observed to be significantly reduced in springtime, when it is expected to be highest. Although, in response to high NH3 deposition large algivorous taxa do not proliferate as was anticipated, and mixotrophic taxa abundance decreases could not be linked primarily to NH3. This research demonstrates the continued potential of testate amoebae as highly informative peatland bioindicators.